Background Concentrations

A successful wetland treatment system is also a successful living ecosystem containing vegetation and related biota. The life and death cycles of this natural biota produce residuals that can then be measured as BOD5, TSS, nitrogen, phosphorus, and fecal coliforms. It is, therefore, not possible for these wetland systems to produce a zero effluent concentration of these materials; some residual background concentration will always be present. Typical concentrations of these constituents are presented in Table 6.9. These background concentrations are not composed of wastewater constituents, but their concentrations may be indirectly

related to the system loadings. A wetland system receiving a nutrient rich wastewater is likely to produce a higher background level than a natural wetland receiving clean water. The background concentrations can also vary on a seasonal basis because of the seasonal occurrence of plant decomposition and the variability in bird and wildlife activity.